As is well known, the valves known as "ball" valves are composed of a valve body having a cylindrical cavity, into which lead two or more ducts connected to the supply of fluids to be distributed or intercepted, according to requirements, and of a ball inside the cylindrical cavity having an axial or cruciform duct and capable of being operated from outside. The ball is mounted between the inlet and deliver ducts in such a way as to dispose the axial duct of the ball in alignment with the inlet and delivery ducts or to close one or the other of these ducts, and also to bring into communication with one another the various channels for a specific distribution of the fluid.
The problem that arises in this type ball valves is the ring seats which surround the ball and which must make a seat both between the inlet and outlet ports in both directions and between both the ports and the control shaft leading to the outside.
The seatings are not subject to being compressed between the fixed and movable part, except during initial assembly, for which reason any wear must be avoided which might give rise to play between the parts, which cannot be taken up.
The seats are also subject both to high temperatures, such as those of saturated and superheated steam, and to high differential pressures, while in these conditions also it must be possible to operate them without the need to apply excessive torque.